x86/paravirt: Remove unused paravirt_disable_iospace()

The last use of paravirt_disable_iospace() was removed in 2015 by
commit d1c29465 ("lguest: don't disable iospace.")

Remove it.

Note the comment above it about 'entry.S' is unrelated to this
but stayed when intervening code got deleted.

Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20250303004441.250451-1-linux@treblig.org